PAGET’S DISEASE OF BONE: SYMPTOMS, DIAGNOSIS, TREATMENT AND MORE

Paget's disease of bone is a chronic disease that affects the normal remodeling process of bones. Also known as osteitis deformans, it is a relatively ordinary condition^[1] with an estimated global prevalence of 1.5-8.3%. Despite its prevalence, many are still unfamiliar with this condition and its potential complications.

This article sheds light on Paget's disease of bone, delving into potential causes and symptoms, risk factors, diagnosis, treatment options, and the latest research and advancements in managing the condition.

Understanding the Causes and Symptoms

Paget's disease of bone arises from abnormal bone remodeling, which is the process of bone turnover or breakdown and replenishment. Bone breaks down at a faster rate in those with the condition. The bone cells are over-sized with up to 50 times more nuclei (the nucleus of the cell holding genetic material), and there are more of them than in healthy bone tissue.

The rapid breakdown of bone provokes rapid bone growth and turnover, 6-7 times faster than average bone turnover. The new growth is disorganized, larger, and more fragile, causing deformity and increasing fracture vulnerability^[2].

Paget's disease of bone is often confused with other bone diseases, such as osteoporosis and arthritis. While these conditions may result from Paget disease and share some similar symptoms, they are distinct in their causes and treatment options.

The bones most commonly affected in Paget’s disease include the spine, skull, long bones in the legs, and pelvic girdle.

There are two types of Paget's disease: monostotic and polyostotic.^[3]

1. Monostotic Paget disease: This type is localized, affecting only one or a few bones.
2. Polyostotic Paget disease: This is multicentric, impacting multiple bones throughout the body.

The frequency of each type is unknown, although one survey reveals that polyostotic disease held a 72% prevalence amongst a sample population with the disease^[4].

The exact cause of this abnormal bone remodeling is still unknown, yet it is likely a combination of genetic and environmental factors. Mutations in the genes SQSTM1, TNFRSF11A, and TNFRSF11B are associated with 10-50% of cases that run in families and 5-30% of independent occurrences^[5]. Other genes implicated include CSF1 and TM7SF4. These mutations affect proteins and precursor molecules involved in bone breakdown and growth.

Research suggests that combinations of the following environmental factors may contribute to causing Paget's disease:

• Viral infections from the paramyxovirus family^[6], including parainfluenza, mumps, measles, and respiratory syncytial virus, can contribute. Not all individuals with Paget disease show evidence of a previous infection. Yet, a higher degree of viral mRNA and genetic changes are prevalent in affected tissues, some of which have the condition.
• Vitamin D deficiency
• Environmental factors such as excessive toxin or radiation exposure
• Bone overuse

Who is at Risk?

While anyone can develop Paget's disease of bone, certain risk factors may increase individual odds of developing the condition. These include:

• Age: Paget's disease is more common in individuals over 50 years old.
• Gender: Men are more likely to develop Paget's disease than women.
• Family History: Having a family history of Paget's disease increases the risk of acquiring the condition. Studies have shown that 15-40% of individuals with Paget's disease have a family history of the condition. Not all gene mutations responsible for the disease are known.
• Ethnicity: Paget's disease prevalently occurs in specific regions such as North America, Australia, New Zealand, and Europe among individuals of Anglo-Saxon ancestry. However, it is not widely prevalent in Asia, Africa, and Scandinavia.

Common Symptoms

The most frequent symptom of Paget's disease of bone is unexplained bone pain, which can be mild or severe. Other symptoms often include^[7]:

• Bone deformities, such as bowing of the legs or curvature of the spine
• Enlarged or misshapen bones
• Joint pain and stiffness near affected bones
• Headaches and hearing loss (if the skull is affected)
• Numbness, tingling, or weakness (if the spine is affected)
• Fatigue and weakness (if the legs are affected)

It is important to note that some people with Paget's disease may not experience any symptoms at all, and the condition may only be discovered incidentally during a routine X-ray or blood test.

What are the Complications of Paget's Disease of Bone?

If left untreated, Paget's disease of bone can lead to several complications, including:

• Fractures and Deformities: The weakened and enlarged bones in individuals with Paget's disease are more prone to fractures, especially in weight-bearing bones such as the hips and legs. This vulnerability can affect the outcome of surgery and increase the risk of complications.
• Movement issues: Bone deformities and pain can lead to difficulties with walking, significantly if the leg bones are affected.
• Osteoarthritis: The abnormal bone growth in Paget's disease can put pressure on joints and contribute to their wear and tear. Prolonged wear and tear leads to osteoarthritis, which causes joint pain and stiffness.
• Nerve Compression: Bone enlargement can compress the nerves running through an affected area and cause neurological manifestations such as numbness, tingling, or peripheral weakness in the arms and legs. In rare cases, this affects hearing, vision, and other body functions.
• Heart Failure: In rare cases, Paget's disease can affect the heart by placing extra strain on blood vessels and the heart, leading to heart failure.
• Bone Cancer: While Paget's disease itself is not a form of cancer, it can increase the risk of developing bone cancer in the affected bones.

Diagnosis

Diagnosing Paget's disease of bone is challenging, as the symptoms can overlap with other bone conditions. However, several tests can help confirm a diagnosis:

• X-ray: An X-ray can show the characteristic bone changes associated with Paget's disease, such as enlarged and misshapen bones.
• CT Scan: A CT scan can provide more detailed images of the affected bones and help determine the severity of the condition.
• Bone Scan: During a bone scan, the patient receives an injection containing a small amount of radioactive material, which the bones absorb. Areas of increased bone activity, indicative of Paget's disease, show on a computer interface as bright spots after special equipment detects the radioactive material.
• Alkaline Phosphatase Blood Test: Individuals with Paget's disease often have elevated levels of alkaline phosphatase, (an enzyme found in the bones), in their blood. A simple blood test can measure these levels and help confirm a diagnosis.

In some cases, a bone biopsy may be done to examine the structure of the bone under a microscope, aiding in the diagnosis.

Additional tests may find hyperuricemia and hyperparathyroidism due to increased bone turnover.

Treatment Options

While there is no cure for Paget's disease of bone, there are several treatment options available to manage the symptoms and prevent complications.

• Pain Relief: Over-the-counter pain medications, can control the pain associated with Paget's disease. In more severe cases, prescription pain medication may be necessary.
• Bisphosphonates: Bisphosphonates are a medication that can help slow down the bone remodeling process and reduce the risk of fractures. They are often used in treating Paget's disease, particularly zoledronic acid, and show efficacy in managing symptoms^[8].

Calcium and vitamin D supplementation are advisable for those on bisphosphonates to ensure adequate intake.^[9] Speak to a nutritionist about supplementation for maintaining optimal bone health and turnover.

Surgery

In cases where the bones are severely deformed or fractured, surgery may be necessary to correct the deformities and stabilize the bones.

Surgery can also alleviate nerve compression and resultant neurological signs, such as peripheral numbness or tingling.^[10]

Physical Therapy

Physiotherapy is the standard option for pain management, improving bone and muscle strength, and increasing range of motion. Common strategies include^[11]:

• Strength training
• Manual therapy
• Joint mobilization
• Exercises to improve range of motion

Low-impact exercises, like walking, swimming, and cycling, are ideal for individuals with Paget's disease.

Assistive devices, a healthy diet, and peer support groups are also helpful.

Prognosis and Life Expectancy

With proper treatment and management, individuals with Paget's disease can live a fulfilling life and have a similar life expectancy to those without the condition. However, it is essential to monitor the condition and seek treatment for any complications that may arise.

Can I Prevent Paget's Disease?

While there is no known way to prevent Paget's disease, maintaining a healthy lifestyle and avoiding known triggers, such as viral infections, may help reduce your risk of developing the condition.

Latest Research and Advancements

Paget's disease of bone remains a lesser understood condition, with researchers puzzling over potential mechanisms, including gene mutations and factors responsible for them.

Ongoing research aims to diagnose the condition quickly, identify new treatments that can offer further relief, and potentially reverse the condition. In recent years, improvements to imaging techniques and minimally invasive surgeries have enhanced diagnosis and treatment outcomes for those with the disease.

Other developments include:

• Targeted therapies: Researchers are designing new therapies that target specific molecules involved in developing Paget's disease. These drugs may have fewer side effects than traditional treatments.
• Denosumab: This medication is also effective in treating Paget's disease. It works by inhibiting the RANK ligand, which is essential for bone formation and resorption. Denosumab is usually prescribed for bone cancer and osteoporosis, yet it has helped a few patients with Paget's disease of bone^[12]. Clinical trials that prove its efficacy and safety for Paget's disease are currently lacking.
• Genetic testing: Genetic testing can pinpoint individuals at risk for developing Paget's disease with a high specificity. This information can aid in developing personalized treatment plans. Some genetic tests are currently under development^[13], yet they require further refinement as they cannot identify all cases of Paget's disease of bone.

Conclusion

Paget's disease of bone is a chronic condition that affects the normal remodeling process of bones. While there is no cure, several treatment options are available to manage the symptoms and prevent complications. Early diagnosis and treatment can enhance the outlook and quality of life for individuals with Paget's disease. By working closely with healthcare providers, individuals with Paget's disease can follow a personalized strategy that meets their needs and improves their overall health and well-being.

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